1. Field of the Invention
This invention relates, generally, to sound-producing devices, and more particularly relates to such devices activated by electromagnetic radiation.
2. Description of the Prior Art
Singing tubes, as they are known, have been studied in scientific laboratories engaged in wave motion and sound research. The application of heat to a metal gauze member placed in the lower half of a vertically oriented tube with open ends causes the air contained within the tube to resonate at a characteristic fundamental frequency dictated by the length of the tube, producing sound. The laboratory tube is normally formed of brass or other opaque material, has ends which terminate in a plane normal to the vertical axis of the tube, and contains a single gauze member. The source of heat is normally a propane flame formed by a burner means.
It is believed that air currents rise from the gauze member when it is heated. In view of the porosity of the gauze member, air below it also rises, is heated periodically as it passes through such hot gauze member, and exits the tube through the top thereof in a continuous stream. Thus, a stream of air is established that enters the bottom of the tube at ambient temperatures and exits the tube at its top in a heated condition. If the heated gauze member were impervious to air, the upwardly directed air flow obviously could not be established.
The "singing tube", as it is known to acoustic researchers, has heretofore been studied as a single unit, there being no known musical instruments that have been formed by grouping a plurality of the tubes in a single location. Nor have the metal gauze members, or generators, been heated by focused sunlight or designed to be heated by focused sunlight through transparent cylindrical walls. Nor has a single tube been fitted with a plurality of generator members, enabling a single tube to resonate at more than one characteristic frequency. Nor has a single tube been provided with ends cut on an angle to the vertical axis of the tube, thereby rendering the sound generating capacity of the tube sensitive to, or dependent upon, the direction of ambient air currents.